Shape memory alloys may be utilized in rotary actuators to provide a torque to rotate an object against an applied load with a minimum of moving parts. For example, a shape memory alloy element may physically transform from a first configuration to a second configuration upon being heated, such that the transition from the first configuration to the second configuration includes a rotary motion and/or generates the torque, which may be harnessed to rotate a rotary element from a first rotary position to a second rotary position. To return the rotary element to the first position from the second position after heating the shape memory alloy element, traditional shape memory alloy actuators simply may be cooled.
A shape memory alloy element may be trained to exhibit a two-way shape memory effect, in which the shape memory alloy element may reversibly and repeatedly operate between a first, or cold, configuration and a second, or hot, configuration without an external bias source. For example, a shape memory alloy element may be trained to exhibit a two-way shape memory effect so as to reversibly and repeatedly rotate a control surface of an aerodynamic model with respect to an airstream in a wind tunnel. While the two-way shape memory effect generally is stable under external loads applied in the training direction (i.e., the direction toward the cold configuration), applying a load in a direction opposite the training direction may result in a degradation of the two-way shape memory effect, and a shape memory alloy receiving such a load may lose an ability to return to its cold configuration. Thus, there exists a need for improved bi-directional rotary shape memory alloy element actuator assemblies, and systems and methods including the same.